1. Field of the Invention
This invention relates to a seal device for sealing a shaft by a seal lip, particularly to a seal device for sealing high pressure fluid by a seal lip against the high pressure thereof, wherein the sealing face of the seal device is configured not to deform abnormally when a shaft is fittingly inserted through the seal lip, so that the sealing face maintains to seal with its sharp face pressure.
2. Description of the Related Art
There has been a lip seal device 100 as the related art 1 of the present invention, as shown in FIG. 7.
FIG. 7 shows a half sectional view of the lip seal device 100. This lip seal device 100 is used for the compressor of a car cooler. Accordingly, this type of the lip seal device 100 is constituted in consideration of carbon dioxide gas as the fluid to be sealed, which has been adopted as an alternative of chlorofluorocarbon gas in view of the effect on the environment. The lip seal device 100 is therefore configured, as shown in FIG. 7.
In FIG. 7, the lip seal device 100 has a seal lip 101 that extends aslope toward the sealed fluid side A from a base section 102 in which an reinforcing ring 103 is embedded. At the distal end section 104 of the extended seal lip 101 is provided a sealing face 104a that closely contacts with the circumferential surface of a rotary shaft 113. A garter spring 105 for tightening the sealing face 104a is fitted in an annular groove that is provided in the outer surface of the end section 104. The axial position and dimensions of the sealing face 104a must be determined exactly and appropriately, relative to the annular groove in which the garter spring 105 is fitted.
Between the inner surface of the seal lip 101 and the rotary shaft 113 on the atmosphere side A is disposed a metal backup ring 106 in contact with or close to the seal lip 101. Additionally, on the atmosphere side A of the backup ring 106, an annular lip 107 of resin material that is conformed to the backup ring 106 is also disposed in the same way of the backup ring 106. Further, a support ring 109 is also disposed on the atmosphere side A of the annular lip 107. Then the backup ring 106, the annular lip 107 and the support ring 109 are sandwiched together by a retainer ring 110 having an inverted U-shape in cross section, resulting in a seal section 108 as a whole, for supporting the seal lip 101.
As the seal section 108 is located in parallel with the seal lip 101 and supports it against the pressure of the sealed fluid, the seal section 108 and the seal lip 101 cooperate to seal the fluid.
In this related art 1, the seal section 108 for supporting the seal lip 101 is disposed separately from and parallel to the seal lip 101. Accordingly, in view of the relationship between the tightening force of the garter spring 105 and the support force of the backup ring 106, if the seal lip 101 is incorrectly combined with the seal section 108 it is difficult to exactly mate the sealing face 104a with the surface of the rotary shaft 113 so as to secure to perform sealing ability with a face pressure. Furthermore, as the seal lip 101 is separated from the seal section 108, they must be fabricated individually, which causes the increase in the production cost.
In the manufacturing processes, the axial distance between the sealing face 104a at the distal end of the seal lip 101 and the annular groove must be exact. However, it is difficult to secure the distance to be uniform, because the seal lip 101 made of rubber is deformable.
Also, the backup ring 106 and the seal lip 101 must be combined exactly. If the backup ring 106 is forced to press against the seal lip 101, the inside diameter of the seal lip 101 is enlarged beyond the outside diameter of rotary shaft 113. This causes the sealing ability to worsen.
There has been a shaft seal device 200 as the related art 2 of the present invention, as shown in FIG. 8.
The shaft seal device 200 is constituted as shown in FIG. 8. FIG. 8 shows a half sectional view of the shaft seal device 200. This shaft seal device 200 is used for the compressor of a car cooler, in which the fluid to be sealed is carbon dioxide gas. This shaft seal device 200 is constituted, as a whole, similarly to the seal device 100 of the related art 1. However, the purpose for use of the backup ring 206 of the shaft seal device 200 is different from that of the backup ring 106 in the related art 1. In other words, it is disclosed in the related art 2 that a seal lip 201 and a seal section 208 are made into a body for the purpose of preventing the sealed fluid from passing through.
In this shaft seal device 200, a cylindrical seal lip 201 is formed so as to extend from the tight-fitting section 202 having an outer circumferential corrugated seal portion 207. The seal section 208 of resin is disposed on the atmosphere side A of the seal lip 201.
A metal sheet ring 206 is disposed between the seal lip 201 of rubber and the seal section 208 of resin, because the seal lip 201 allows carbon dioxide gas to penetrate therethrough. Accordingly, the metal sheet ring 206 is intervened between the seal lip 201 and the seal section 208 in such a way that it is attached to cover almost entire surface of the seal lip 201 on the atmosphere side A thereof.
However, it is difficult, in view of both the structure and strength, for the backup ring 206 of thin metal sheet to bear the seal lip 201 always in close contact with the rotary shaft 213. In other words, it is difficult for the constitution for preventing such penetration of carbon dioxide gas, to expand the seal lip 201 with the backup ring 206 against the strong elastic force applied to the sealing face 204a of the seal lip 201. Because the sealed gas becomes rapidly apt to penetrate by elongating and expanding the seal lip 201.
It is also difficult for the thin backup ring 206 having the purpose of avoiding such penetration to prevent the sealing face 204a subject to the pressure of the sealed fluid from deforming to be flat in pressure contact with the rotary shaft 213.
Additionally, as the backup ring 206 is a thin metal sheet, it is also difficult, in view of the structure, for the backup ring 206 to resiliently expand and retain the seal lip 201 so that the sealing face 204a of the seal lip 201 is optimally in pressure contact with the rotary shaft 213.
In the related arts as has been described, the sealed fluid will leak if the inner surface or the sealing face 104a, 204a of the seal lip 101, 201 are in close contact with the outer surface of the rotary shaft 113, 213 without a sharp face pressure when the seal device 100, 200 is fitted around the rotary shaft 113, 213. Accordingly, the seal device 100, 200 having the sealing face 104a, 204a the inside diameter of which is smaller than the outer diameter of the rotary shaft 113, 213 is only press-fitted to the rotary shaft 113, 213.
However, when the rotary shaft 113, 213 is press-fitted in the sealing face 104a, 204a of the seal lip 101, 201 made of rubber, it is difficult to make the sealing face 104a, 204a be optimally in close contact with the rotary shaft 113, 213, due to a large frictional resistance of rubber. Additionally, due to the frictional resistance, the seal lip 101, 201 is forced to elongate in the insertion direction, resulted in abnormal fitting in the state that the sealing face 104a, 204a is twisted around the rotary shaft 113, 213. In this state, the angle formed between the circumferential surface of the rotary shaft 113, 213 and the sealing face 104a, 204a is reduced. Therefore, the sealing face 104a, 204a fitting to the rotary shaft 113, 213 seals while a larger area of the sealing face 104a, 204a is in contact with the rotary shaft 113, 213. In this fitting state, the sealing ability is worsened due to the large contact area, thereby to cause the sealed fluid to leak.
When the sealing face 104a, 204a is forced to press strongly against the rotary shaft 113, 213, the contact area is increased and thus the inclination of the face pressure becomes gentle, thereby also to cause the sealing ability to be worsened. The frictional effect of the increased contact area promotes to produce sludge to reduce the sealing ability.
Further, when the pressure of the sealed fluid becomes high in the conditions described above, the friction between the sealing face 104a, 204a increases to facilitate the wear on the sealing face 104a, 204a. 
The present invention is made in view of the problems as has been described and a technical problem to be solved by the present invention is to provide a seal device in which the sealing face of the seal device comes in close contact with the rotary shaft with a sharp face pressure when the rotary shaft is inserted in the seal device.
Another technical problem is to provide a seal device with sealing ability improved by contacting closely the seal section with the rotary shaft in the state of a sharp face pressure. Further another technical problem is to maintain the contact area of the sealing face not to be enlarged under the pressure applied to the sealing face from the sealed fluid and to prevent the wear on the sealing face.